Mastering the Language of Gemstone Faceting

The world of gem cutting has a bewildering vocabulary all its own. Student gemologists and novice cutters as well as aficionados of jewelry design can benefit from a glossary of faceting terms. Let's dive into the fascinating lexicon of gemstone faceting.

Aligning and Measuring

Alignment refers to positioning the stone so that the crown break facets match up with the pavilion break facets at the girdle after transferring the stone. Calipers are used to measure the dimensions of a cut stone. Analog and digital angle scales on faceting machines allow users to adjust the quill to precise angles, from 1 degree to 1/100th of a degree.

Cutting Techniques

CAM (Center Point Angle Method) and CLAM (Corner Locator Angle Method) are pre-form cutting techniques. The former involves cutting 3 or 4 temporary pavilion facets to establish the culet, then cutting corresponding girdle facets. The latter cuts two pavilion facets that make a line from the culet to the corner of the pre-form.

Gemstone Properties

Cleavage and fracture refer to the way a stone breaks - along a flat plane or an uneven surface. Color absorption and color change are fascinating phenomena in gems. Some stones like alexandrite can shift hue under different light sources, while others like tanzanite can be heat-treated to alter their color.

Faceting Vocabulary

The crown is the top portion of a cut stone, while the pavilion is the bottom. The critical angle is the pavilion angle at which light will be totally reflected, producing excellent sparkle. The culet is the bottom point or facet. Faceters, not cutters, work on colored stones, using techniques like dopping, charging laps, and cheating facets to achieve the desired result.

Measuring and Grading

Carat is the unit of weight for gems, not to be confused with karat (gold purity) or carrot (the vegetable). Hardness is measured on the Mohs scale from 1 to 10, with diamond being the hardest at 10. Loupe-clean means no flaws are visible under 10x magnification, while eye-clean means no flaws are visible to the naked eye.

Mastering the language of gemstone faceting opens up a whole new world of appreciation for the art and science behind these dazzling creations. Whether you're a seasoned collector or just starting to explore the fascinating field of lapidary, this glossary of terms is sure to enhance your understanding and enjoyment of these captivating gems.